1. Field of the Invention
The present invention relates to a resolver apparatus and an angle detection device and method of the same. More specifically, the present invention relates to an angle detection device and method of a resolver raising the detection precision and a resolver apparatus having the angle detection device and a resolver.
2. Description of the Related Art
FIG. 1 is a view of the configuration of a resolver body 7. The resolver body 7 is provided with a SIN winding 4, a COS winding 5 arranged mechanically offset by 90 degrees from this SIN winding 4, and a rotor winding 6. An object of detection of the rotational angle (or rotational position), for example, a shaft of a motor (not shown), is connected to the rotor winding 6. As the resolver, a two-phase excitation single-output system and a single-phase excitation two-output system are known. Below, for example, the two-phase excitation single-output system will be illustrated. A SIN winding voltage and a COS winding voltage are supplied to the SIN winding 4 and the COS winding 5, whereby a signal corresponding to the rotational angle of the object for which the rotational angle is being detected is detected from the rotor winding 6. Namely, when the object for which the rotational angle is being detected rotates, the rotor winding 6 rotates and a linkage flux state of the SIN winding 4 and the COS winding 5 changes. By extracting and processing that state from the rotor winding 6 as a rotor winding voltage S6, the rotational angle or rotational position of the object for which the rotational angle is being detected can be detected.
A resolver has the advantage that it is mechanically durable and can withstand even deleterious environments, therefore is being utilized for detection of various rotational angles (or rotational positions). However, a resolver has the defect that the detection error is large and the detection precision is low when compared with an encoder used for the detection of a rotational angle of a servo motor etc. For this reason, the practice has been to correct the detection error.
FIG. 2 is a graph showing an example of the detection error of the resolver. The abscissa shows the actual angle, and the ordinate shows the detection angle. A line CV1 indicates the actual accurate angle having no error, while a curve CV2 fluctuating above and below the line CV1 indicates a detection angle including detection error. The detection error of the resolver is determined in magnitude and direction of error with respect to the angle as illustrated in FIG. 2. Although there is reproducibility, there are large individual differences in the resolvers concerning the detection error. The waveform of the detection error illustrated by the curve CV2 also differs for each resolver. Accordingly, the practice had also been to perform processing for correcting detection error so as to raise the detection precision for individual resolvers as well.
FIG. 3 is a diagram showing the circuit configuration of a conventional estimated angle generation circuit 14A. The estimated angle generation circuit 14A has a table number acquisition portion 35, an error angle data reference portion 38, and a subtraction portion 37. The error angle data reference portion 38 has a ROM 38a. For example, in advance, as illustrated in FIG. 2, actual angles and detection angles are found, the detection errors are detected (calculated), and waveform signals of the detected errors are stored as a table in the ROM 38a. When actually correcting detection error to calculate an angle, the table number acquisition portion 35 generates an address signal S35 for reading out a waveform signal of error stored in the ROM 38a based on the angle detection signal S11 detected from the rotor winding of the resolver, and the error angle data reference portion 38 reads out the corresponding error angle data S36 from the ROM 38a based on the address signal S35. Further, the subtraction portion 37 subtracts the error angle data S36 from the angle detection signal S11 to correct the angle detection signal S11. The angle corrected in this way is utilized as, for example, an angle detection signal of a position feedback control system or speed feedback system.
As another method of correcting the detection error of a resolver, for example, Japanese Patent Publication (A) No. 11-118520 discloses, as a prior art for a resolver apparatus of the single-phase excitation two-output system, a method of calculating the angle by a tracking system using an analog circuit and, for improving this method using an analog circuit, a method of detecting the angle by digital signal processing using a Fourier transform.
The Fourier transform method for the latter resolver of the single-phase excitation two-output system will be explained next. Processing for inputting an (S-sin) signal, an (S-cos) signal, and an excitation signal (sin ωt) of the single-phase excitation two-output system resolver and converting them by A/D conversion, multiplying the A/D converted (S-sin) signal and (S-cos) signal in a digital manner to find a multiplication result SA1, and multiplying the A/D converted excitation signal (sin ωt) by cos ωt to find a multiplication result SB1 is repeated by exactly the number of times of the sampling number n. In the same way, the cos signal is multiplied with sin ωt to find the multiplication results CA2 and CB2. An absolute value of sin θ is found from absolute values of SA1 and SB1, an absolute value of cos θ is found from absolute values of CA2 and CB2, a tan−θ of sin θ and cos θ is found, and a digital angle θ is found from a tan− table.
The method explained with reference to FIG. 3 has the problem that the processing for detecting detection errors from the relationships between accurate actual angles and detection angles including detection error in advance for each of the resolvers, organizing the results, and storing the same, for example, as a table linking the actual angles and detection angles as illustrated in FIG. 2 in, for example, the ROM 38a of the error angle data reference portion 38 illustrated in FIG. 3 must be carried out manually, so is very troublesome. In particular, in actual use, there is the restriction that the resolvers and angle detection devices must be in one-to-one correspondence. The above work must be carried out for individual resolvers by using such angle detection devices, so there is an inconvenience that this technique is not suited for application to general purpose servo motors and servo amplifiers.
If determining a correction value of detection error for each resolver each time, for example, a large inertia is attached to the servo motor, a rotation inertia of that inertia is utilized to realize a constant rotation with no pulsation, actual angles and detection angles are measured at that constant rotation to detect detection errors included in the detection angles, and the detected detection errors are analyzed and stored as a table linking actual angles and detection angles in a memory of a computer. Using the above method, detection error is actually corrected for the detection angle. Measurement of the detection error from the actual angle and the detected angle in a state where there is no fluctuation of the rotation by using inertia is advantageous for improving the precision of the correction. However, the motor measured for rotational position for example often rotates when the power is turned on in a state where it is attached to a robot or conveyer. In practice, attachment of such inertia to a motor etc. is often difficult.
Japanese Patent Publication (A) No. 11-118520 discloses only a Fourier transform method using signal processing by a computer by software. In the signal processing by software, however, too long a processing time is taken for performing various complex processing such as Fourier transforms, so it is not possible to detect the angle of an object for angle detection in real time. Accordingly, for example, this cannot be applied to applications for quickly detecting the rotational angle of a rotating body rotating at a high speed, for example, a motor.
While not disclosed nor suggested in Japanese Patent Publication (A) No. 11-118520, even if using a high speed processor, for example, a digital signal processor (DSP), in place of a usual computer to realize faster processing, this method would not be suitable for angular detection in real time. Further, the price of the system would become expensive. Further, the method disclosed in Japanese Patent Publication (A) No. 11-118520 covers a resolver of the single-phase excitation two-output type and uses two detection signals from the resolver, so if applying the method disclosed in Japanese Patent Publication (A) No. 11-118520, the Fourier transform and other signal processing become complex.
From above, it has been desired to provide an angle detection device of a resolver overcoming the issues explained above.